Universitat de Vic - Universitat Central de Catalunya. Facultat de Ciències i Tecnologia

Abstract:

Aim of study: In the Mediterranean region, yew (Taxus baccata L.) usually grows with other tree species in mixed forests. Yew
recruitment and juvenile growth may depend on the structure of the forest and the net balance between competition for soil water
and nutrients with neighbors and facilitation that these neighbors exert by protecting the plants from direct sun exposure. This study
aims, at a regional scale, to analyze the structure of forests containing yew, and, on an individual level, to analyze the effect of the
surrounding vegetation structure on the performance of yew juveniles.
Area of study: The structural typologies of yew populations were defined based on field inventories conducted in 55 plots distributed
in 14 localities in the North-Eastern (NE) Iberian Peninsula, covering a wide range of yew distribution in the area. In a
second step, an analysis of neighboring species’ effects on juveniles was conducted based on the data from 103 plots centered in
yew juveniles in five localities.
Main Results: A cluster analysis classified the inventoried stands into four forest structural types: two multi-stratified forests
with scattered yew and two yew groves. Multiple regression modeling showed that the δ13C measured in last year’s leaves positively
relates to the basal area of conifer neighbors, but negatively with the cover of the yew crown by other trees.
Research highlights: At a stand-level, the density of recruits and juveniles (625 ± 104 recruits ha–1, 259 ± 55 juveniles ha–1) in
mixed forests was found to be higher than that on yew dominant stands (181 ± 88 recruits ha–1 and 57 ± 88 juveniles ha–1). At an
individual-level, the water stress (estimated from leaf δ13C) of yew juveniles seems alleviated by the crown cover by neighbors
while it increases with the basal area of conifers. Yew conservation should focus on selective felling for the reduction of basal area
of neighbors surrounding the target tree, but avoid affecting the canopy cover to contribute to enhanced yew juvenile growth.